1. Field of the Invention
The present invention generally relates to manufacture of millwork made of plastic, such as polyurethane, and, more particularly, is concerned with a molding apparatus having upper and lower composite mold/press units with replaceable mold cavity forming components for producing millwork products having different shaped profiles.
2. Description of the Prior Art
Due to the high cost of custom manufacture of wood and the persistent maintenance problems of wood in terms of rotting, cracking, warping, splintering and insect infestation, millwork for entry systems, window treatments, louvers, molding and architectural enhancements made of plastic, such as polyurethane, is increasingly being utilized in both commercial and residential construction, as well as, in historical restoration. Millwork made of plastic, sometimes referred to as formed millwork, is easy to handle, saws cleanly for miter cuts, and can be applied with construction adhesives and/or nails and screws. Such millwork does not need sanding or sealing and can be patched with ordinary (non-solvent) wood fillers. Furthermore, such millwork is substantially maintenance free in that its white acrylic prime finish will not peel and it is UV-stabilized to resist sun fading and readily accepts latex paint. Such millwork has the feel, density, and workability of wood while avoiding the aforementioned problems associated with wood. For convenience in terminology used hereinafter, the term millwork, formed millwork, molded millwork, or plastic millwork refers to millwork made of a plastic material, such as polyurethane, and are used interchangeably throughout this specification.
Heretofore, the process for manufacturing millwork has been simple and straight-forward piece work although very labor intensive and time-consuming. For any given end-product, the present manufacturing process involves, first, making a wood pattern of the desired product and, next, making a silicon rubber mold from the wood pattern which is the negative shape of the product. Then, the rubber mold is placed in a frame-box carrier which supports the mold such that the mold is confined to the shape of the pattern since otherwise the rubber could stretch and flex when it is filled. Following thereafter, the mold is sprayed with a releasing agent which will allow the molded product to be released from the mold and which will also provide a very smooth finish on one side of the product. The releasing agent actually is capable of forming a smooth finish skin on the product. Next, a suitable liquid plastic, such as polyurethane, is poured into the mold and a lid is placed over the open face of the mold. The liquid plastic can expand several times in volume due to an exothermic reaction that will occur in the polyurethane. The closed mold is then placed in a press for about thirty minutes (exothermic reaction time) such that the expandable polyurethane due to its confinement in the closed mold will increase in density as well as volume to provide the desired end-product. After the time has expired, the closed mold is removed from the press, its lid is removed and the product is removed from the mold. The product is now finished off by cleaning its edges, patching any pin holes therein and spray painting its top surface. The life of a normal rubber mold is approximately two hundred pours depending upon the complexity of the specific part, then the construction of a new rubber mold is required from the original pattern. Additionally, any given rubber mold is also limited to a small quantity of parts produced per day because of the heat build up in the rubber mold due to exothermic reaction of the injected material. It can be readily appreciated from the above description that the present manufacturing process is only capable of increasing production accompanied by greater labor utilization at increasing cost.
As the use of certain ones, such as interior and exterior molding, of the millwork pieces continue to increase, there is a need for introduction of innovations in the millwork manufacturing process which will lead toward the goal of achieving increased production of pieces at lower unit costs to be able to satisfy a growing market demand at a reasonable profit.